1. Field of the Invention
The present invention relates to an indicator panel for instrument and a method of manufacturing the same.
2. Description of Related Art
Conventionally, an indicator device, e.g., an instrument panel, is provided in a vehicle. Generally, the indicator device includes a panel and a light source. The panel includes a design portion having scales and letters, and the light source is provided at a backside of the panel. In the panel, the design portion except for the scales and the letters is made of an opaque portion, in which a light is not transmitted. The scales and the letters are made of a translucent portion, in which a light is transmitted. Thereby, the translucent portion, e.g., the scales and the letters, can be displayed clearly by illuminating the panel with the light source at night.
An indicator panel for instrument is usually manufactured by printing the opaque portion (solid concealing image portion) on a surface of a transparent substrate made of resin, e.g., polycarbonate, in a screen-printing. The screen-printing is a printing method, in which ink is printed on a substrate through a screen after an image from a print data is drawn on the screen. The screen-printing has an advantage that a dark opaque portion can be printed at one time.
Further, in the screen-printing, a solvent drying type ink or heat hardening type ink is mainly used. Because the screen-printing is a monochromatic printing, multilayer printings using different color inks are required for forming a multicolored design. In this case, a process number and a process time for the screen-printing are increased. Furthermore, in the screen-printing, a design is restricted because an accuracy of a printing position and a resolution are generally low.
Except for the screen-printing, a digital printing method such as a laser printing, an electrophotography printing, a thermoelectric printing and an inkjet printing is used in other fields, e.g., office automation printer field. These printings can perform a direct printing on the indicator panel for instrument without forming the screen. Thus, these printings may be better for a small lot printing than the screen-printing.
Among the digital printing methods, the inkjet printing rapidly becomes common in the office automation printer field, because the initial cost is low and the resolution is high due to a simple structure. The inkjet printing is performed by jetting ink from a computerized head nozzle.
JP-A-2002-156252 discloses an indicator panel for a display device, in which the panel is formed by the inkjet printing on a transparent substrate made of resin. U.S. Pat. No. 6,856,478 (corresponding to JP-2004-A-286459) discloses an indicator panel, in which an ink receiving layer and a light shielding printed layer are laminated on a substrate by the inkjet printing.
However, when the inkjet printing is performed on a transparent substrate made of resin, e.g., polycarbonate, using the solvent drying type ink, which is conventionally used in the inkjet printing on a paper substrate, the ink does not penetrate the substrate. Therefore, when droplets of the ink are overprinted by an inkjet printing device, the droplets volume left on the substrate may be large. Thus, especially in the overprinting case, a predetermined sharp and clear design cannot be formed due to a transudation of the inks.